This invention relates to connecting devices for connecting together a plurality of elongated building materials such as frame bars.
For connecting together a plurality of elongated building materials such as frame bars, it has been known, as shown in FIG. 17, to set an L-shaped metal structure 30 on side surfaces of the bars 20 to be connected and to fasten it to them by using bolts 33 and nuts (not shown). Connections thus made are unsightly because the connecting structures 30 are openly visible. If the cross-sectional shape of the bars to be connected together is not quadrangular but polygonal with a larger number of sides, furthermore, the width of the side surfaces where the connecting structure can be fastened becomes smaller, and the strength of connection is adversely affected.
It is therefore an object of this invention to provide connecting devices capable of connecting together elongated building materials such as frame bars more securely.
It is another object of this invention to provide such connecting devices having less protrusions at the joint.